This proposal involves the peroxidase enzymes, typified in this case by yeast cytochrome c peroxidase, and the monomeric oxygen- binding proteins, typified by the Glycera dibranchiata monomer hemoglobins. Goals of this proposal include using isolated, natural proteins, recombinant wild-type proteins and recombinant mutant proteins maximize NMR characterization and quantify heme- site chemistry. In the case of cytochrome c peroxidase, we are proposing to build upon our significant success during the past year in making proton NMR assignments using a variety of 2D NMR methods in order to expand these assignments. Specifically created site-specific mutant proteins will be useful in this effort. Isotope labeling (15N & 13C) will be used as an assignment tool. In addition, characterization of the properties of the individual mutant proteins will be carried out by NMR. In the case of the Glycera dibranchiata monomer hemoglobins, whose architecture is virtually superimposable to that of sperm-whale myoglobin, we propose to NMR with isotope labelling for the goal of making "total" assignments. We intend to demonstrate NMR methods for assaying structural changes induced by specific mutations. We propose to use five specific site-mutants designed to modify ligand binding dynamics in a predictable manner, and design mutants predicted to modify heme--globin interactions in anticipated ways. In addition we intend to use these results and others in order to test our ability to design and create mutants designed for a specific purpose, based upon inferences from the crystal structure.